• Complaints from neighborhood residents or within the factory attributed to low-frequency sound from undetermined equipment in the factory
• The equipment generating low-frequency sound is known, and measures are desired
• An estimate is desired of low-frequency sound levels at site boundaries, or the extent of propagation beyond the site

Sounds having an extremely low frequency between 1 and 100 Hz are called low-frequency sound. Sounds between 1 and 20 Hz are specially called infrasound in Japan. The primary equipment responsible for low-frequency sound is as given in the following table.
Impact from low-frequency sounds can roughly be classified into two types. The first has mental and physical impacts, characterized by unpleasantness, oppressive feeling or the like. The other concerns material impacts like rattling of windows or doors.

The following are some past examples of INC low-frequency sound attenuation measures:

Expansion-type silencer	Sound wave is attenuated by being reflected at portions where the duct cross-sectional shape changes
Side branch silencer	One or more branches are attached to main pipe. Branch length is adjusted so that the sound wave phase in the branch is reverse to that in the main pipe to attenuate low-frequency sound.
Phase control	Sound waves are emitted from two difference sources at reversed phase to each other to attenuate low-frequency sound.

When looking to investigate the impact of multiple low-frequency sound sources upon the surrounding areas, propagation simulations of low-frequency sound with appropriate software are useful. INC has developed its own low-frequency sound simulation software and provides it as a solution to INC customers.